In the manufacture of an electronic device such as a semiconductor device, a substrate processing apparatus is used. A gas for processing a substrate is supplied into a processing vessel of the substrate processing apparatus from a gas supply system. In general, the gas supply system is configured to supply one or more gases selected from multiple kinds of gases into the processing vessel of the substrate processing apparatus. Further, the gas supply system is equipped with multiple flow rate controllers for controlling flow rates of the multiple kinds of gases individually.
As such a flow rate controller, there is known a pressure type flow rate controller. The flow rate controller of this type is operated to reduce a difference between a set flow rate as a target value and a calculation flow rate calculated from a pressure measurement value of a pressure gauge of the flow rate controller. However, the calculation flow rate of the flow rate controller may have a big error from an actual output flow rate of the flow rate controller as it is used. For this reason, the output flow rate of the flow rate controller needs to be calculated. As a method of calculating the output flow rate of the flow rate controller, there is known a so-called build-up method. The build-up method is described in Patent Document 1.
In the build-up method, a gas is supplied into the processing vessel of the substrate processing apparatus via a flow rate controller as a measurement target, and an output flow rate of the flow rate controller as the measurement target is calculated from an internal pressure of the processing vessel, an internal temperature of the processing vessel and a previously known internal volume of the processing vessel.
Patent Document 1: Japanese Patent No. 5,286,430
Since, however, the internal volume of the processing vessel is very large, the conventional build-up method includes an error factor. For example, the conventional build-up method is affected by a temperature difference within the processing vessel and/or a change of the processing vessel with the lapse of time. Though it may be considered to use a method of calculating the output flow rate of the flow rate controller with a flow rate measuring device provided within the gas supply system without using the processing vessel, such a method causes a cost increase of the gas supply system.
Thus, it is required to calculate the output flow rate of the flow rate controller by using the components previously provided in the gas supply system.